Sakata S, Hayes J M, McTaggart A R, Evans R A, Leckrone K J, Togasaki R K
Department of Geological Sciences, Indiana University, Bloomington 47405, USA.
Geochim Cosmochim Acta. 1997;61(24):5379-89. doi: 10.1016/s0016-7037(97)00314-1.
For the cyanobacterium Synechocystis UTEX 2470, grown photoautotrophically to a logarithmic stage of growth, the total lipid extract is depleted in 13C by 4.8% relative to average biomass. Depletions observed for acetogenic (straight-chain) lipids range from 7.6 (hexadecanoic acid) to 9.9% (a C16 n-alkyl chain bound in a polar-lipid fraction), with a mass-weighted average of 9.1%. Polyisoprenoid lipids fall into two isotopic groups, with phytol, diplopterol, and diploptene depleted by 6.4-6.9% and bishomohopanol (produced from the extracts by the preparative degradation of bacteriohopanepolyol) depleted by 8.4%. Analysis of the pattern of depletions indicates that two carbon positions in each C5 biomonomer leading to polyisoprenoid products are probably depleted in 13C relative to average biomass. The depletion of bacteriohopanepolyol relative to other polyisoprenoids can be ascribed to changes that occur over the life of each cell: (1) the 13C content of carbon flowing to lipid biosynthesis decreases as the cell size increases and (2) a greater proportion of the bacteriohopanepolyol which, unlike other polyisoprenoids, is present mainly in the cytoplasm rather than in membranes and is synthesized when cells are larger. Chlorophyll a is depleted relative to average biomass by O.7%. Given the observed depletion of 13C in phytol, the heteroaromatic, chlorophyllide portion of chlorophyll must be enriched in 13C by 2.7%. This enrichment is large relative to that in chlorophyllides produced by eukaryotes and may be related to a parallel enrichment of 13C in cyanobacterial glutamic acid. As in many previous investigations of cyanobacterial lipids, long-chain n-alkanes (C22-C29) are found in the extracts. They are, however, enriched in 13C relative to biomass and have isotopic compositions suggesting that they are contaminants of petrochemical origin. Available results indicate that cyanobacterial lipids will be depleted relative to dissolved CO2 that has served as a carbon source by 22-30% and that a wider range of depletions will be characteristic of eukaryotic products. The absence of long-chain n-alkanes in cyanobacteria reduces the possibility that petroleum ever formed from pre-eukaryotic sedimentary debris.
对于光合自养生长至对数生长期的集胞藻UTEX 2470，其总脂质提取物中的13C相对于平均生物量减少了4.8%。产乙酸（直链）脂质的13C减少量在7.6%（十六烷酸）至9.9%（结合在极性脂质部分的C16正烷基链）之间，质量加权平均值为9.1%。聚异戊二烯脂质分为两个同位素组，植醇、双翅醇和双翅萜的13C减少了6.4 - 6.9%，而双高藿烷（通过细菌藿烷多元醇的制备性降解从提取物中产生）的13C减少了8.4%。对减少模式的分析表明，相对于平均生物量，每个导致聚异戊二烯产物的C5生物单体中的两个碳位置可能在13C中减少。细菌藿烷多元醇相对于其他聚异戊二烯的减少可归因于每个细胞生命过程中发生的变化：（1）随着细胞大小增加，流向脂质生物合成的碳的13C含量降低；（2）与其他聚异戊二烯不同，细菌藿烷多元醇的更大比例主要存在于细胞质中而非膜中，并且在细胞较大时合成。叶绿素a相对于平均生物量减少了0.7%。鉴于观察到植醇中13C的减少，叶绿素的杂芳族叶绿素酸部分的13C必须富集2.7%。相对于真核生物产生的叶绿素酸中的富集，这种富集程度较大，并且可能与蓝藻谷氨酸中13C的平行富集有关。与之前许多对蓝藻脂质的研究一样，提取物中发现了长链正构烷烃（C22 - C29）。然而，它们相对于生物量在13C中富集，并且同位素组成表明它们是石化来源的污染物。现有结果表明，蓝藻脂质相对于用作碳源的溶解CO2将减少22 - 30%，并且更广泛的减少范围将是真核生物产物的特征。蓝藻中不存在长链正构烷烃降低了石油从前真核生物沉积残骸形成的可能性。
